Thanks a lot for playing and the detailed feedback!
Dying in 1985 in the beginning is normal, at some point you get back to 1985 with your party of old people to help the previous party of your younger selves to fight back. Immobilise can be useful when you've got your 5 characters against a single one.
Enemies never respawn, maybe you got this impression because some appeared in front of you after "falling" from a nearby rooftop. While they don't come from the opposite side of the map they can indeed come from afar enough, the chance they get alerted is inversely proportional to the actual distance via a path they can follow, although when they're not on the same floor then they only come when they're already very close.
The game is definitely not easy though.